1. Field of the Invention
The present invention relates to a light converging optical system in which rays of light planned to be incident on a reflecting optical-spatial modulator element are converged for the purpose of forming an image from the converged rays. Also, the present invention relates to an image displaying apparatus in which rays of light converged in the light converging optical system are incident on the reflecting optical-spatial modulator element to modulate the rays of light and to display an image reproduced from the modulated light. Also, the present invention relates to a projection image displaying apparatus, such as a digital light processing (DLP(trademark)) projector, in which a large number of micro-minors disposed in a reflecting optical-spatial modulator element in a two-dimensional matrix are respectively switched from an xe2x80x9conxe2x80x9d state (or an xe2x80x9coffxe2x80x9d state) to an xe2x80x9coffxe2x80x9d state (or the xe2x80x9conxe2x80x9d state) to modulate rays of light incident on the reflecting optical-spatial modulator element and to display an image reproduced from the modulated light.
2. Description of Related Art
A digital micro-mirror device (DMD(trademark), hereinafter, simply called DMD) is, for example, used for an image displaying apparatus having a projection type screen. The DMD is formed of a reflection type semiconductor device and functions as a reflection type optical-spatial modulator element. An optical signal is intensity-modulated in the DMD by spatially changing the intensity of the light signal according to digital image information. The DMD used for the image displaying apparatus differs from a transmission type liquid crystal which receives light on a rear surface from a light converging optical system and outputs an intensity-modulated optical signal from a front plane to a projection type optical system. In the DMD used for the image displaying apparatus, a light converging optical system and a projection type optical system are disposed on a side of a reflecting surface of the DMD to form a reflecting optical system. On the reflecting surface of the DMD, a large number of micro-mirrors respectively having a size of 16 square xcexc m are disposed in a two-dimensional matrix shape at pitches (or intervals) of 17 xcexcm. The number of micro-mirrors is equal to the number of pixels forming an image plane of a screen and is larger than hundreds of thousands. Each micro-mirror corresponds to one pixel. Therefore, when light radiated from a lamp light source is received as an optical signal on the reflecting surface of the DMD through a converging lens, the intensity of each optical signal is changed in the corresponding micro-mirror according to digital image information to obtain an intensity-modulated optical signal. The intensity-modulated optical signal is output from the reflecting surface of the DMD as an image information signal according to a time on-off control.
FIG. 37 is a partially enlarged schematic view of a reflecting surface of the DMD. FIG. 38 is an explanatory view of an operation of an inclination control performed for a micro-mirror.
In FIG. 37 and FIG. 38, 101 indicates a reflecting surface of the DMD. 102 indicates each of a plurality of square shaped micro mirrors disposed on the reflecting surface 101 of the DMD. Ar denotes a rotation axis of each micro-mirror. The inclination of the micro mirror 102 on the rotation axis Ar is controlled. The rotation axis Ar is placed on one diagonal line of the micro mirror 102. When a principal ray of a light flux is incident on the micro mirror 102, an incident direction of the principal ray projected on the reflecting surface 101 is parallel to the other diagonal line of the micro mirror 102 also, the incident direction of the principal ray is set to make an angle of 20 degrees to a normal n0 of the reflecting surface 101.
A binary control of on-off is performed for each micro-mirror 102 according to a control voltage based on digital image information stored in a memory, and the micro-mirror 102 is inclined on the rotation axis Ar. The inclination angle of each micro-mirror 102 is set to +10 degrees or xe2x88x9210 degrees, and a reflection direction of a light flux incident on the micro-mirror 102 is changed from a direction corresponding to an xe2x80x9conxe2x80x9d state (or xe2x80x9coffxe2x80x9d state) to a direction corresponding to an xe2x80x9coffxe2x80x9d state (or xe2x80x9conxe2x80x9d state). An operation of the inclination control performed for each micro-mirror 102 will be described below.
In FIG. 38, the reflecting surface 101 of the micro mirrors 102 is placed on the plane of horizontal. 102a indicates one micro-mirror inclined by an inclination angle of +10 degrees to the reflecting surface 101. That is, the micro-mirror 102a is set to an xe2x80x9conxe2x80x9d state. 102b indicates a micro-mirror inclined by an inclination angle of xe2x88x9210 degrees to the reflecting surface 101. That is, the micro-mirror 102a is set to an xe2x80x9coffxe2x80x9d state. Therefore, each micro-mirror 102 make an angle of +10 degrees or xe2x88x9210 degrees to the reflecting surface 101 as the micro-mirror 102a or 102b. The micro-mirrors 102a and 102b are inclined on the rotation axis Ar. In this embodiment, the inclination on the rotation axis Ar in the clockwise direction is indicated by a positive inclination angle, and the inclination on the rotation axis Ar in the counterclockwise direction is indicated by a negative inclination angle.
103 indicates an incident principal ray of a converged incident light flux. The incident principal ray 103 radiated from a light converging optical system (not shown) is incident on the micro-mirror 102a or 102b. 104a indicates an outgoing principal ray of an outgoing light flux. The incident principal ray 103 reflected on the micro-mirror 102a goes out from the micro-mirror 102a as the outgoing principal ray 104a. 104b indicates an outgoing principal ray of another outgoing light flux. The incident principal ray 103 reflected on the micro-mirror 102b goes out from the micro-mirror 102b as the outgoing principal ray 104b. 105 indicates a screen. 105a indicates each of a plurality of pixels of the screen 105. The outgoing principal ray 104a reflected on the micro-mirror 102a is received in one pixel 105a of the screen 105. 106 indicates a projection lens of a projecting optical system. The projection lens 106 is placed between the reflecting surface 101 of the DMD and the screen 105, and the outgoing principal ray 104a transmitted through the projection lens 106 is projected on one pixel 105a of the screen 5.
The incident principal ray 103 makes an angle of 20 degrees to the normal n0 of the reflecting surface 101 and is incident on the micro-mirror 102a or the micro-mirror 102b. In cases where it is intended to project light on one pixel 105a of the screen 105, the inclination angle of one micro-mirror 102 corresponding to the pixel 105a is controlled to +10 degrees according to a control voltage. In this case, the incident principal ray 103 makes an angle of 10 degrees to a normal nA of the micro-mirror 102a and is incident on the micro-mirror 102a. Therefore, the incident principal ray 103 is reflected toward the direction of the normal n0 of the reflecting surface 101 as the outgoing principal ray 104a according to the law of reflection, the outgoing principal ray 104a passes through the projection lens 106, the outgoing principal ray 104a is received in the pixel 105a of the screen 5, and the pixel 105a is brightened (or set to xe2x80x9conxe2x80x9d state).
In contrast, in cases where it is intended not to project light on one pixel 105a of the screen 105, the inclination angle of one micro-mirror 102 corresponding to the pixel 105a is controlled to xe2x88x9210 degrees according to another control voltage. In this case, the incident principal ray 103 makes an angle of 30 degrees to a normal nB of the micro-mirror 102b and is incident on the micro-mirror 102b. Therefore, the incident principal ray 103 is reflected as the outgoing principal ray 104b toward a direction making an angle of 40 degrees to the normal n0 of the reflecting surface 101 according to the law of reflection. Because the outgoing principal ray 104b is directed out of an pupil of the projection lens 106, the pixel 105a is not brighten by the outgoing principal ray 104b (or set to xe2x80x9coffxe2x80x9d state).
As is described above, in the DMD, the on-off control is performed for each micro-mirror 102 to incline the micro-mirror 102 by each of the angles of xc2x110 degrees to the reflecting surface 101. In this case, because the switching of the inclination angle from +10 degrees (xe2x88x9210 degrees) to xe2x88x9210 degrees (+10 degrees) is performed within a time period of 10 xcexcsec, a light flux incident on the micro-mirror 102 can be modulated as an optical signal in the DMD at high speed.
As is realized from FIG. 38, because the micro-mirror 102 is controlled to be inclined at each of the angles of xc2x110 degrees, the outgoing principal ray 104b makes an angle of 60 degrees to the incident principal ray 103 in case of the xe2x80x9coffxe2x80x9d state. In contrast, the outgoing principal ray 104a makes an angle of 20 degrees to the incident principal ray 103 in case of the xe2x80x9conxe2x80x9d state and is positioned nearest to the incident principal ray 103. Therefore, when light is converged by a lens to produce a light flux incident on the DMD from the light, to prevent the overlapping of the incident light flux with an outgoing light flux reflected on the micro-mirror 102a, an F-number F (F=f/d, the symbol f denotes a focal length of the lens, and the symbol d denotes a diameter of a stop of the lens) of the lens is restricted by the inclination angles of xc2x110 degrees.
The reason of the restriction of the F-number will be described in detail with reference to FIG. 39A and FIG. 39b. 
FIG. 39A is a view showing both a conical incident light flux incident on one micro-mirror 102 at a diverging angle of 10 degrees corresponding to the F-number of Fi=3 and a conical outgoing light flux reflected on the micro-mirror 102 of the xe2x80x9conxe2x80x9d state. The constituent elements, which are the same as those shown in FIG. 38, are indicated by the same reference numerals as those of the constituent elements shown in FIG. 38.
In FIG. 39A, 107 indicates an incident light flux formed in a conical shape and set to a diverging angle of 10 degrees corresponding to an F-number Fi=3 (that is, a diverging angle of 10 degrees). Here, a diverging angle of a light flux is defined as an angle between a principal ray of the light flux and a ray of the light flux furthest from the principal ray. Also, when parallel light is changed to a light flux having a diverging angle xcex8 by a lens of an F-number F, the F-number F of the lens is expressed according to an equation F=1/(2xc3x97tan xcex8)). Therefore, in this specification, it is described that the F-number F corresponds to the diverging angle xcex8 of the light flux. Also, Though the diverging angle xcex8 of the light flux is generally expressed by xe2x80x9csteradianxe2x80x9d of a solid angle, a diverging angle of a light flux projected on a plane is considered in this specification for convenience of explanation, and the diverging angle is expressed by xe2x80x9cdegreexe2x80x9d in this specification.
108 indicates an outgoing light flux formed in a conical shape corresponding to the F-number of Fi=3. The vertex of the conical shape of each light flux is positioned in the center of the micro-mirror 102. The diverging angle of each light flux is equal to 10 degrees. The incident light flux 107 indicates a light flux converging on the incident side when the light flux 107 is observed from the center of the micro-mirror 102. The outgoing light flux 108 indicates a light flux diverging on the outgoing side when the light flux 108 is observed from the center of the micro-mirror 102.
107a and 107b indicate incident rays included in the incident light flux 107 respectively. 108a and 108b indicate outgoing rays included in the outgoing light flux 108 respectively. The incident ray 107a is positioned nearest to the outgoing principal ray 104a among rays of the incident light flux 107. The incident ray 107b is positioned furthest from the outgoing principal ray 104a among rays of the incident light flux 107. The outgoing ray 108a is positioned nearest to the incident principal ray 103 among rays of the outgoing light flux 108. The outgoing ray 108b is positioned furthest from the incident principal ray 103 among rays of the outgoing light flux 108.
Therefore, the incident rays 107a and 107b are positioned on the most-outer side of the incident light flux 107 and respectively make an angle of 10 degrees to the incident principal ray 103. The incident rays 107a and 107b are incident on the micro-mirror 102 (or 102a) inclined by the angle of +10 degrees and are reflected on the micro-mirror 102. The reflected incident rays 107a and 107b go out as the outgoing rays 108a and 108b. 
109a is a plane perpendicular to the incident principal ray 103 of the incident light flux 107. 109b is a plane perpendicular to the outgoing principal ray 104a of the outgoing light flux 108. A sectional view of both the incident light flux 107 taken along the plane 109a and the outgoing light flux 108 taken along the plane 109b is shown in FIG. 39B. In FIG. 39B, for convenience of explanation, it is regarded that the plane 109a is parallel to the plane 109b. 
As shown in FIG. 39A and FIG. 39B, in case of the micro-mirror 102 (or 102a) corresponding to the xe2x80x9conxe2x80x9d state, the incident principal ray 103 makes the angle of 20 degrees to the outgoing principal ray 104a. Therefore, in cases where a diverging angle xcex8 of the incident light flux 107 is set to a fixed value in any direction centering around the incident principal ray 103, the incident ray 107a and the outgoing ray 108a passes through the same normal nA of the micro-mirror 102 in case of the diverging angle xcex8 equal to 10 degrees.
Therefore, in cases where the diverging angle xcex8 of the incident light flux 107 exceeds 10 degrees, a portion of the incident light flux 107 including the incident ray 107a undesirably interferes with a portion of the outgoing light flux 108 including the outgoing ray 108a. In other words, a lighting optical system providing the incident light flux 107 structurally overlaps with the projecting optical system receiving the outgoing light flux 108. To avoid the overlapping of the optical systems with each other, the diverging angle xcex8 is set to 10 degrees, and the incident light flux 107 is prevented from interfering with the outgoing light flux 108.
Because the F-number of the lighting optical system corresponding to the diverging angle xcex8 is expressed by 1/(2xc3x97tan xcex8) by using the refractive index of the air equal to 1, the minimum value of the F-number is equal to about 3 in case of the diverging angle xcex8 set to 10 degrees. In general, the F-number indicates the brightness of the optical system. As the F-number becomes smaller (or as the diverging angle xcex8 becomes larger), the brightness of the optical system is increased. Therefore, in the conventional light converging optical system structured so as to converge light onto the micro-mirror 102 controlled to the inclination angles of xc2x110 degrees, in cases where a light flux formed in a conical shape of the diverging angle xcex8=10 degrees (or the F-number equal to about 3) is incident on the micro-mirror 102, the most-brightened optical system can be obtained.
Next, a conventional image displaying apparatus using a light converging optical system for the DMD will be described below.
FIG. 40 is a view showing the configuration of a conventional image displaying apparatus using a light converging optical system.
In FIG. 40, 111 indicates a light emitting element for emitting light. 112 indicates a parabola reflector figured in a shape of a paraboloid of revolution. The light emitting element 111 is placed at a focal point of the parabola reflector 112, and the light emitted from the light emitting element 111 is reflected on the parabola reflector 112 so as to be changed to parallel light. A lamp light source is composed of the light emitting element 111 and the parabola reflector 112. 113 indicates a converging lens for changing the parallel light obtained in the lamp light source to a light flux. 114 indicates a color wheel for separating light of each primary color from the light flux obtained in the converging lens 113. In this prior art, a single-plate method is used. That is, red light (R), green light (G) and blue light (B) are separated one after another from the light flux in time division by using one color wheel 114. Thereafter, the red light (R), the green light (G) and the blue light (B) are radiated to the DMD 121 in time division one by one, and a color space formed of the three primary colors R, G and B is reproduced. However, it is applicable that a three-plate method be adopted to obtain the three primary colors R, G and B. That is, red light (R), green light (G) and blue light (B) of the three primary colors are separated from three light fluxes respectively by using three plates, and the red light (R), the green light (G) and the blue light (B) are independently radiated to the DMD 121.
115 indicates an integrator rod formed in a rectangular parallelepiped figure. In the integrator rod 115, the light flux color-separated in the color wheel 114 is received in an incident end plane, the light flux is changed to a plurality of light fluxes, intensities of the light fluxes are equalized, and the light fluxes having a uniform intensity distribution are output from an outgoing end plane of the integrator rod 115. 116 indicates a relay lens for relaying the light fluxes output from the integrator rod 115. 118 indicates a bending mirror for bending optical paths of the light fluxes. 119 indicates a field lens for properly adjusting directions of principal rays included in the incident light fluxes.
120 indicates a total internal reflection (TIR) prism. To prevent a light flux incident on the projecting optical system from being not received in an entrance section of the projecting optical system, only the incident light fluxes are totally reflected by the TIR prism 120, and a plurality of outgoing light fluxes are straightly transmitted through the TIR prism 120 without loosing any outgoing light flux. Therefore, the light converging optical system and the projecting optical system are structurally separated from each other.
121 indicates the DMD. The micro-mirrors 102 are disposed on the reflecting surface 101 of the DMD 121. 122 indicates a projection lens for forming an image from the light fluxes intensity-modulated in the DMD 121. 123 indicates a rear projection type screen. The light fluxes denoting the image formed in the projection lens 122 are received in a rear surface of the rear projection type screen 123, and the image is displayed on the screen 123. 124 indicates an optical axis of the constituent elements 111, 112, 113, 114, 115, 116, 118, 119, 120, 121, 122 and 123 of the conventional image displaying apparatus.
Next, an operation of the conventional image displaying apparatus will be described below.
The light emitting element 111 is made in a figure of a point light source within the limits of the possible and is disposed at a focal point of the parabola reflector 112. Therefore, light emitted from the light emitting element 111 is reflected by the parabola reflector 112 and is output as parallel light. The parallel light output from the parabola reflector 112 is converged onto a focal point of the converging lens 113 by the converging lens 113 as a light flux figured in a conical shape corresponding to the F-number of F1=1 (or a diverging angle xcex81=30 degrees made to the optical axis 124). Because it is required to make small a converged diameter of the light flux in the use of the color wheel 114, the F-number of F1=1 is generally adopted as an optimum F-number.
In the color wheel 114, the light flux is converged at a small converging spot, and a specified primary color is selected from the three primary colors of the light flux. Thereafter, because the focal point of the converging lens 113 is positioned at the incident end plane of the integrator rod 115, the light flux of the selected primary color is incident on the incident end plane of the integrator rod 115. In the integrator rod 115, the light flux of the selected primary color is reflected on an internal side surface of the integrator rod 115 many times so as to produce a plurality of light fluxes and to equalize intensities of the light fluxes. Therefore, the light fluxes output from the outgoing end plane of the integrator rod 115 have a distribution of an almost uniform intensity in the outgoing end plane. Also, each light flux output from the integrator rod 115 is diverged at the F-number of F1=1 in the same manner as the light flux incident on the integrator rod 115.
Thereafter, the light fluxes are incident on the TIR prism 120 through the relay lens 116, the bending mirror 118 and the field lens 119. The light fluxes incident on the TIR prism 120 are reflected in the inside of the TIR prism 120 and are radiated to the micro-mirrors 102 of the DMD 121. Therefore, image information is given to the light fluxes in the DMD 121 according to digital image information, and intensity-modulated light fluxes having the image information are output from the DMD 121. In this case, the F-number of Fi=3 is selected for the light fluxes radiated to the micro-mirrors 102 of the DMD 121 as an optimum F-number.
Thereafter, the intensity-modulated light fluxes having the image information are again transmitted through the TIR prism 120 and are projected onto the screen 123 through the projection lens 122.
In the conventional image displaying apparatus, a size ratio of the incident end plane (or the outgoing end plane) of the integrator rod 115 to the reflecting surface of the DMD 121 is determined according to both the F-number (F1=1) of the light flux incident on the incident end plane of the integrator rod 115 and the F-number (Fi=3) of the light fluxes incident on the reflecting surface 101 of the DMD 121.
FIG. 41 is an explanatory view showing the relation in size between the integrator rod 115 and the DMD 121. The constituent elements, which are the same as those shown in FIG. 40, are indicated by the same reference numerals as those of the constituent elements shown in FIG. 40. The bending mirror 118, the field lens 119 and the TIR prism 120 are omitted for convenience of explanation, and the function of the field lens 119 is included in that of the relay lens 116. Also, though the light fluxes are actually incident on the DMD 121 at an angle (or an angle of incidence) of 20 degrees to the optical axis 124 of the DMD 121, because only incidence conditions of the light fluxes incident on the DMD 121 are described with reference to FIG. 41, a principal ray incident on the DMD 121 at right angles (or at an incidence angle of 0 degree) is additionally shown in FIG. 41.
In FIG. 41, w denotes a side length of the incident end plane and a side length of the outgoing end plane in the integrator rod 115 a denotes an optical path length between the integrator rod 115 and the relay lens 116. b denotes an optical path length between the relay lens 116 and the DMD 121. W denotes a side length of the reflecting surface of the DMD 121.
Also, xcex81 denotes a diverging angle of a light flux output from the outgoing end plane of the integrator rod 115 with respect to the optical axis 124. xcex8i denotes a diverging angle of a light flux incident on the reflecting surface of the DMD 121 with respect to the optical axis 124. In general, when each of the angles xcex81 and xcex8i is not set to a large value, the relation w/W=a/b=xcex8i/xcex81=F1/Fi is satisfied.
To use the color wheel 114, xcex81=30 degrees (F1=1) is inevitably set. Also, xcex8i=10 degrees (Fi=3) is set according to the use condition of the DMD 121 controlled to the inclination angles of xc2x110 degrees. Therefore, the relation w/W=a/b=xcex8i/xcex81=F1/Fi=⅓ is obtained. In other words, in the optical system shown in FIG. 41, the light flux is radiated from the integrator rod 115 having the side length w to the DMD 121 having the side length W through the relay lens 116 at the magnification W/w=3. Therefore, when the size of the reflecting surface of the DMD 121 and the angles xcex81 and xcex8i are determined, the size of the incident end plane and the outgoing end plane of the integrator rod 115 is automatically determined.
As is described above, because the conventional image displaying apparatus using the light converging optical system for the DMD 121 has the above-described configuration, the F-number of the light flux incident on the DMD 121 is restricted according to the inclination angle of the DMD 121. In this case, it is difficult to enlarge the incident end plane of the integrator rod 115 and to prevent the light flux from being not received in the integrator rod 115 as a result, a loss of the light flux to be received in the integrator rod 115 cannot be reduced, and a problem has arisen that the brightness of the image obtained in the optical system is undesirably restricted.
This problem will be described below in detail.
FIG. 42A is a view of the lamp light source composed of the light emitting element 111 and the parabola reflector 112. FIG. 42B shows an intensity distribution of rays converged onto the incident end plane of the integrator rod 115. FIG. 42C shows a positional relation between a projected image of the lamp light source and the incident end plane of the integrator rod 115.
As shown in FIG. 42A, in the light converging optical system applied to the conventional image displaying apparatus, rays of light are emitted in all directions from the light emitting element 111 made in a figure of a point light source within the limits of the possible, the rays of light are changed to a light flux set to the F-number of F1=1 (or the diverging angle xcex8 of 30 degrees to the optical axis 124) in the parabola reflector 112 and the converging lens 113, and the light flux is converged onto the incident end plane 115a of the integrator rod 115. In this case, as shown in FIG. 42B, an intensity distribution 125 of rays of the light flux converged onto the incident end plane of the integrator rod 115 is formed in rotation symmetry on the optical axis 124.
Assuming that the lamp light source composed of the light emitting element 111 and the parabola reflector 112 has an infinitely small size, an area of the converging spot formed on the incident end plane of the integrator rod 115 is reduced to almost zero, and all the converged light flux is received in the integrator rod 115. However, because the light emitting element 111 has a certain size, when rays of light emitted in all directions are converged at the diverging angle of 30 degrees, the lamp light source is magnified and projected according to the same principle as that of a relay lens, and an image of the lamp light source is projected onto the incident end plane of the integrator rod 115.
As shown in FIG. 42C, the projected image 125A of the lamp light source is larger than the incident end plane 115a of the integrator rod 115. Therefore, all rays of light emitted from the lamp light source are not received in the integrator rod 115, a portion of the rays of light are converged out of the incident end plane 115a of the integrator rod 115 and are lost. As a result, light sent from the whole light converging optical system to the DMD 121 is undesirably lowered.
Also, in cases where the size of the incident end plane of the integrator rod 115 is increased to decrease an amount of light not received in the integrator rod 115, because the F-number (F1=1) of the light flux output from the converging lens 113 and the F-number (Fi=3) of the light flux incident on the DMD 121 are determined, it is required to increase the size of the DMD 121 so as to satisfy the relation of the magnification W/w=3. Therefore, a manufacturing cost of the conventional image displaying apparatus is undesirably increased.
Also, in the conventional image displaying apparatus, rays of light diverged at a wide diverging angle are incident on the projection lens 122. In this case, because a portion of the rays of light are reflected on the reflecting surface 101 of the DMD 121 or the TIR prism 120 according to the specular reflection, a specular reflection component of the light is undesirably incident on the projection lens 122 as stray light. Therefore, a problem has arisen that a contrast of the image is degraded.
Next, another prior art will be described.
Image displaying apparatuses have been improved to heighten a light use efficiency. In cases where the light use efficiency is heightened, an electric power provided to a lamp light source can be reduced, and the expected life span of image displaying apparatuses can be lengthened.
FIG. 43 is a view of the configuration of another conventional image displaying apparatus. FIG. 44 is a view of the configuration of a color wheel used for the conventional image displaying apparatus shown in FIG. 43.
In FIG. 43 and FIG. 44, 201 indicates a light source. 202 indicates a reflector. 203a and 203b indicate condensing lenses respectively. 204 indicates an integrator rod. 204in indicates an incident end plane of the integrator rod 204. 204out indicates an outgoing end plane of the integrator rod 204. 205 indicates a disk shaped color wheel. 205r indicates a red color filter of the color wheel 205. 205b indicates a blue color filter of the color wheel 205. 205g indicates a green color filter of the color wheel 205. 206 indicates a relay lens. 207 indicates a TIR prism. 208 indicates a DMD. 209 indicates a projection lens. 210 indicates a screen.
Next, an operation of the conventional image displaying apparatus shown in FIG. 43 will be described below. The color wheel 205 is rotated. When white light is emitted from the light source 201, the white light is reflected by the reflector 202 so as to be changed to parallel white light. This parallel white light is converged onto the incident end plane 204in of the integrator rod 204 as a white light flux by the condensing lenses 203a and 203b and is received in the integrator rod 204. The white light flux received in the integrator rod 204 is reflected many times in the inside of the integrator rod 204 so as to produce a plurality of white light fluxes and to equalize intensities of the white light fluxes in the outgoing end plane 204out of the integrator rod 204.
Thereafter, in the color wheel 205 with the color filters 205r, 205b and 205g, a plurality of red light fluxes (R), a plurality of blue light fluxes (B) and a plurality of green light fluxes (G) of three primary colors are separated one after another as a plurality of colored light fluxes from the white light fluxes output from the outgoing end plane 204out of the integrator rod 204.
FIG. 45 is a view showing a display condition of three color filters of the color wheel 205 in a single image frame time period. When the color wheel 205 shown in FIG. 44 is rotated, the red color filter 205r, the blue color filter 205b and the green color filter 205g of the color wheel 205 go across the white light one after another in that order every single image frame time period, and the white light is changed to red light, blue light and green light in that order every single image frame time period.
Returning to FIG. 43, the red light fluxes, the blue light fluxes and the green light fluxes separated from the white light fluxes in the color wheel 205 are radiated one after another to the DMD 208 through the relay lens 206 and the TIR prism 207 in the single image frame time period. Thereafter, when a plurality of colored light fluxes are incident on a plurality of micro-mirrors of the DMD 208 set to an xe2x80x9conxe2x80x9d state, the colored light fluxes are reflected in an xe2x80x9conxe2x80x9d direction by the DMD 208 so as to pass through the TIR prism 207, and the colored light fluxes are projected onto the screen 210 by the projection lens 209.
Also, to improve the light use efficiency in the conventional image displaying apparatus shown in FIG. 43, an image displaying apparatus using a light recycling optical system is disclosed in a literature I xe2x80x9cSequential Color Recapture and Dynamic Filteringxe2x80x9d D. Scott Dewald, Steven M. Penn, and Michael Davis, Proc. of SID, pp. 1076-1079, 2001.
FIG. 46 is a view showing the configuration of a conventional image displaying apparatus using a light recycling optical system. FIG. 47 is a view showing the structure of a sequential color recapture (SCR) wheel of the conventional image displaying apparatus shown in FIG. 46. The constituent elements, which are the same as those shown in FIG. 43 and FIG. 44, are indicated by the same reference numerals as those of the constituent elements shown in FIG. 43 and FIG. 44.
In FIG. 46 and FIG. 47, 211 indicates a reflection film disposed on the incident end plane 204in of the integrator rod 204. 211h indicates an aperture of the reflection film 211. 212 indicates a color wheel peculiar to a light recycling optical system. The color wheel 212 is formed of a sequential color recapture (SCR) wheel disclosed in the literature I. 212r, 212b and 212g indicate a red color filter, a blue color filter and a green color filter of the SCR wheel 212 respectively. The color filters 212r, 212b and 212g of the SCR wheel 212 are formed in a volute pattern (or a xe2x80x9cspiral of Archimedesxe2x80x9d pattern).
Next, an operation of the conventional image displaying apparatus shown in FIG. 46 will be described below.
The SCR wheel 212 is rotated. When white light is emitted from the light source 201, the white light is reflected by the reflector 202 so as to be changed to parallel white light. This parallel white light is converged onto the incident end plane 204in of the integrator rod 204 as a white light flux by the condensing lenses 203a and 203b, passes through the aperture 211h of the reflection film 211, and is received in the integrator rod 204. The white light flux received in the integrator rod 204 is reflected many times in the inside wall of the integrator rod 204 so as to produce a plurality of white light fluxes and to equalize intensities of the white light fluxes in the outgoing end plane 204out of the integrator rod 204.
Thereafter, the white light fluxes output from the outgoing end plane 204out of the integrator rod 204 pass through the SCR wheel 212. In this case, the red light fluxes (R), the blue light fluxes (B) and the green light fluxes (G) of three primary colors are simultaneously separated from the white light fluxes in the SCR wheel 212.
FIG. 48 is a view showing the color filters 212r, 212b and 212g of the SCR wheel 212 going across the white light fluxes in a single image frame time period.
As shown in FIG. 48, the color filters 212r, 212b and 212g of the SCR wheel 212 go across the white light fluxes in a scanning direction in the single image frame time period.
Next, an operation peculiar to the light recycling optical system will be described below.
FIG. 49 is a view showing loci of rays of light passing through the integrator rod 204 in cases where the reflection film 211 is not disposed on the incident end plane 204in of the integrator rod 204. FIG. 50 is a view showing loci of rays of light passing through the integrator rod 204 in cases where the reflection film 211 is disposed on the incident end plane 204in of the integrator rod 204. The constituent elements, which are the same as those shown in FIG. 46 and FIG. 47, are indicated by the same reference numerals as those of the constituent elements shown in FIG. 46 and FIG. 47.
In FIG. 49 and FIG. 50, Ll indicates a ray of loss light causing the lowering of a light use efficiency. Lr indicates a ray of recycled light again used.
As shown in FIG. 49, assuming that the conventional image displaying apparatus using a light non-recycling optical system is operated, when the red light (R), the green light (G) and the blue light (B) of three primary colors are separated from the white light in the color filters 212r, 212b and 212g of the SCR wheel 212, colored light other than light of the selected primary color is reflected by the color filter corresponding to the selected primary color in the direction of the incident end plane 204in of the integrator rod 204. Because the reflected colored light goes out from the incident end plane 204in to the outside of the integrator rod 204, the reflected colored light other than light of the selected primary color cannot be used for the display of an image. Therefore, the reflected colored light is lost as the loss light Ll, and the light use efficiency in the case of the color-separation shown in FIG. 49 is almost equal to ⅓.
In contrast, as shown in FIG. 50, the reflection film 211 is disposed on the incident end plane 204in of the conventional image displaying apparatus using the light recycling optical system. Therefore, when the red light (R) separated in the red color filter 212r of the SCR wheel 212, the blue light (B) separated in the blue color filter 212b of the SCR wheel 212 and the green light (G) separated in the green color filter 212g of the SCR wheel 212 simultaneously pass through the SCR wheel 212, the other colored light is reflected on the color filters 212r, 212b and 212g of the SCR wheel 212. In this case, the other colored light is again reflected on the reflection film 211 and propagates toward the outgoing end plane 204out as the recycled light Lr. The recycled light Lr again reaches the SCR wheel 212. When the color of the recycled light Lr matches with one color filter of the SCR wheel 212, the recycled light Lr passes through the SCR wheel 212. Therefore, red light (R), blue light (B) and green light (G) of three primary colors are separated from the recycled light Lr in the SCR wheel 212, and the red light (R), the green light (G) and the blue light (B) separated from the recycled light Lr are used for the display of an image.
Therefore, because the light recycling optical system having the reflection film 211 and the SCR wheel 212 is used for the conventional image displaying apparatus, the light reflected by the SCR wheel 212 can be reused for the display of an image as the recycled light Lr, and the light use efficiency can be improved.
Here, the structure of the SCR wheel 212 differs from that of the color wheel 205, and the color filters 212r, 212b and 212g of the SCR wheel 212 are formed in a volute pattern. Therefore, because the color filters 212r, 212b and 212g are always arranged on the outgoing end plane 204out of the integrator rod 204, each primary color component of the light reflected toward the incident end plane 204in is again reflected on the reflection film 211 and passes through the color filter corresponding to the primary color component. Therefore, the light use efficiency is improved.
Returning to FIG. 46, the red light fluxes, the blue light fluxes and the green light fluxes separated from the white light fluxes in the SCR wheel 212 are simultaneously radiated to the DMD 208 through the relay lens 206 and the TIR prism 207 as colored light fluxes. When a plurality of colored light fluxes are incident on a plurality of micro-mirrors of the DMD 208 set to the xe2x80x9conxe2x80x9d state, the colored light fluxes incident on the micro-mirrors are reflected in an xe2x80x9conxe2x80x9d direction so as to pass through the TIR prism 207, and the colored light fluxes are projected onto the screen 210 by the projection lens 209.
The inventors of this application estimate that the light use efficiency in the conventional image displaying apparatus of FIG. 46 using the light recycling optical system is almost 1.1 times larger than that in the conventional image displaying apparatus of FIG. 43 using the light non-recycling optical system.
However, because the conventional image displaying apparatus shown in FIG. 46 has the above-described configuration, the light use efficiency is only almost 1.1 times larger than that in the conventional image displaying apparatus of FIG. 43. Therefore, a problem has arisen that the light use efficiency cannot be sufficiently improved.
This problem will be described in detail with reference to FIG. 50.
Only light passing through the aperture 211h of the reflection film 211 can be received in the integrator rod 204, and loss light Ll converged by the condensing lenses 203a and 203b on the incident end plane 204in of the integrator rod 204 and reflected on the reflection film 211 cannot be used for the display of an image even though the light recycling optical system is used for the conventional image displaying apparatus. An amount of the loss light Ll depends on the area of the reflection film 211. Therefore, the more the area of the reflection film 211 is increased to reuse the loss light L, the more the light receiving efficiency is lowered. Therefore, the light use efficiency cannot be sufficiently improved.
Also, in the conventional image displaying apparatuses shown in FIG. 43 and FIG. 46, a plurality of micro-mirrors (not shown) are arranged on the DMD 208. Each micro-mirror is inclined by an inclination angle in a clockwise direction or a counter-clockwise direction to direct the light flux reflected on the micro-mirror in the xe2x80x9conxe2x80x9d direction or the xe2x80x9coffxe2x80x9d direction. To prevent the interference between the incident light flux incident on the micro-mirror and the outgoing light flux reflected on the micro-mirror, a diverging angle of the incident light flux corresponding to the F-number is determined according to the inclination angle of the micro-mirror. In this case, because the diverging angle of the light flux incident on the incident end plane 204in of the integrator rod 204 is generally set to 30 degrees, the size of the incident end plane 204in of the integrator rod 204 is determined according to the relation w/W=a/b=xcex8i/xcex81=F1/Fi described with reference to FIG. 40. This size of the incident end plane 204in is called a regular size. Therefore, when the incident end plane 204in of the integrator rod 204 is set to a size larger than the regular size, the diverging angle of an incident light flux incident on the micro-mirror exceeds the inclination angle of the micro-mirror, and a portion of the incident light flux incident on the micro-mirror overlaps with a portion of the outgoing light flux reflected on the micro-mirror. In this case, the incident light flux and the outgoing light flux interfere with each other. Therefore, the incident end plane 204in of the integrator rod 204 is necessarily set to the regular size.
Also, in the conventional image displaying apparatus shown in FIG. 46, the reflection film 211 is disposed on the incident end plane 204in of the integrator rod 204 having the regular size, an area of the aperture 211h of the reflection film 211 cannot be sufficiently enlarged, and the light receiving efficiency of the integrator rod 204 is inevitably reduced due to the area of the reflection film 211 other than the aperture 211h. Therefore, the light use efficiency cannot be sufficiently improved.
Also, because the light source 201 is generally formed of a high pressure mercury lamp, a light emitting area of the light source 201 is determined by an arc size of the light source 201. Therefore, a converged spot of a light flux obtained by the condensing lenses 203a and 203b has a certain size and is larger than the incident end plane of the integrator rod 204. For example, an arc size of the light source 201 is xcfx861.0 mmxc3x971.4 mm (a diameter of 1 mmxc3x971.4 mm length). The inclination angle of each micro-mirror of the DMD 208 is +10 degrees or xe2x88x9210 degrees. A length of a diagonal line of a reflecting surface of the DMD 208 is equal to 0.74 inch (about 18.8 mm). In this case, because the diverging angle of the light flux incident on the integrator rod 204 is equal to 30 degrees which is tree times larger than the inclination angle, the regular size of the incident end plane 204in of the integrator rod 204 is equal to 5 mmxc3x973.8 mm.
FIG. 51 is a view showing the relation between a light receiving efficiency and a light recycle efficiency when the incident end plane 204in of the integrator rod 204 is set to the regular size of 5 mmxc3x973.8 mm. The light receiving efficiency is defined as a ratio of a quantity of light received in the integrator rod 204 to a quantity of light emitted from the light source 201 of the conventional image displaying apparatus shown in FIG. 46. Also, a reference quantity of light passing through the SCR wheel 212 is measured on condition that no reflection film is disposed on the incident end plane 204in of the integrator rod 204, and the light recycle efficiency is defined as a ratio of a quantity of light passing through the SCR wheel 212 of the conventional image displaying apparatus shown in FIG. 46 to the reference quantity of light.
As is shown in FIG. 51, the regular size of the incident end plane 204in of the integrator rod 204 is smaller than a size of a converged spot of the light converged by the condensing lenses 203a and 203b, so that the maximum of the light receiving efficiency is equal to about 75%. When the size of the aperture 211h of the reflection film 211 is enlarged, the light receiving efficiency is increased, but the light recycle efficiency is decreased. Therefore, the light receiving efficiency and the light recycle efficiency are set in the trade-off relation.
FIG. 52 is a view showing a light use efficiency when the incident end plane 204in of the integrator rod 204 is set to the regular size of 5xc3x973.8 mm. The light use efficiency is defined as a product value of the light receiving efficiency and the light recycle efficiency. In this case, the light use efficiency is minimized at the aperture size of about 6.2 mm in diameter (the light recycle efficiency of 1.0 and the light receiving efficiency of 75%), the light use efficiency is normalized to unity at the aperture size of about 6.2 mm by multiplying the light use efficiency by 1/0.75. When the size of the aperture 211h of the reflection film 211 is set to about 93.5 mm, the light use efficiency is maximized. Therefore, the maximum of the light use efficiency is only 1.1 times of that in the conventional image displaying apparatus shown in FIG. 43.
A main object of the present invention is to provide, with due consideration to the drawbacks of the conventional image displaying apparatus, a light converging system in which light is converged so as to be efficiently incident on a reflection type optical-spatial modulator element without being restricted by an inclination angle of each micro-mirror disposed on the reflection type optical-spatial modulator element.
Also, the main object of the present invention is to provide an image displaying apparatus in which the brightness of an image formed by light sent from the light converging system is improved without being restricted by an inclination angle of each micro-mirror disposed on the reflection type optical-spatial modulator element.
Also, a first subordinate object of the present invention is to provide an image displaying apparatus in which a contrast of the image is improved.
Also, a second subordinate object of the present invention is to provide an image displaying apparatus in which a light use efficiency is considerably improved.
The main object is achieved by the provision of a light converging optical system including a converging lens, a light-intensity distribution uniformizing element and a relay optical system. Light emitted from a lamp light source is changed by the converging lens to a first light flux having a first diverging angle corresponding to a first F-number. In light-intensity distribution uniformizing element, the first light flux is changed to a plurality of second light fluxes respectively corresponding to the first F-number, intensities of the second light fluxes are equalized in an outgoing end plane, and the second light fluxes having a uniform intensity distribution are output. In the relay optical system, each second light flux output from the light-intensity distribution uniformizing element is changed to a third light flux having a second diverging angle larger than the inclination angle of each micro-mirror of the reflection type optical-spatial modulator element, and the third light flux of the second diverging angle is relayed to a reflection type optical-spatial modulator element.
The relay optical system includes a first group of lenses, a relay deformed diaphragm and a second group of lenses. A Fourier transformation plane is formed by the first group of lenses. In the Fourier transformation plane, position information indicating positions of rays of the second light fluxes in the outgoing end plane of the light-intensity distribution uniformizing element is transformed into diverging angle information indicating diverging angles of rays of light to an optical axis of the light-intensity distribution uniformizing element. The relay deformed diaphragm is disposed in the neighborhood of the Fourier transformation plane. In the relay deformed diaphragm, the rays of light having the diverging angle information is received from the first group of lenses, a portion of the rays of light functioning as an interference component in the reflection on a micro-mirror set to an xe2x80x9conxe2x80x9d state in the reflection type optical-spatial modulator element is intercepted according to the diverging angle information. In the second group of lenses, the rays of light passing through the relay deformed diaphragm are changed to the third light fluxes of the second diverging angle, and the third light fluxes are output to the reflection type optical-spatial modulator element.
Therefore, the third light fluxes are respectively formed in an asymmetric shape in section. In this case, even though each second light flux is changed to the third light flux having a second diverging angle larger than the inclination angle of each micro-mirror of the reflection type optical-spatial modulator element, because a portion of the rays of light functioning as an interference component in the reflection on a micro-mirror set to an xe2x80x9conxe2x80x9d state in the reflection type optical-spatial modulator element is intercepted by the relay deformed diaphragm, any portion of each third light flux incident on the corresponding micro-mirror does not overlap with a portion of an outgoing light flux reflected on the micro-mirror.
Accordingly, the contrast of an image formed from the third light fluxes can be maintained, and light is converged so as to be efficiently incident on the reflection type optical-spatial modulator element without being restricted by the inclination angle of each micro-mirror disposed on the reflection type optical-spatial modulator element.
The main object is achieved by the provision of an image displaying apparatus including a converging lens, a light-intensity distribution uniformizing element, a relay optical system, a projecting optical system and a screen. Light emitted from a lamp light source is changed by the converging lens to a first light flux having a first diverging angle corresponding to a first F-number. In light-intensity distribution uniformizing element, the first light flux is changed to a plurality of second light fluxes respectively corresponding to the first F-number, intensities of the second light fluxes are equalized in an outgoing end plane, and the second light fluxes having a uniform intensity distribution are output. In the relay optical system, each second light flux output from the light-intensity distribution uniformizing element is changed to a third light flux having a second diverging angle larger than the inclination angle of each micro-mirror of the reflection type optical-spatial modulator element, and the third light flux of the second diverging angle is relayed to the reflection type optical-spatial modulator element. In the reflection type optical-spatial modulator element, the third light fluxes receive image information. Thereafter, the third light fluxes are projected onto the screen by the projecting optical system, and an image is displayed on the screen according to the image information included in the third light fluxes projected by the projecting optical system.
The relay optical system includes a first group of lenses, a relay deformed diaphragm and a second group of lenses. A Fourier transformation plane is formed by the first group of lenses. In the Fourier transformation plane, position information indicating positions of rays of the second light fluxes in the outgoing end plane of the light-intensity distribution uniformizing element is transformed into diverging angle information indicating diverging angles of rays of light to an optical axis of the light-intensity distribution uniformizing element. The relay deformed diaphragm is disposed in the neighborhood of the Fourier transformation plane. In the relay deformed diaphragm, the rays of light having the diverging angle information is received from the first group of lenses, a portion of the rays of light functioning as an interference component in the reflection on a micro-mirror set to an xe2x80x9conxe2x80x9d state in the reflection type optical-spatial modulator element is intercepted according to the diverging angle information. In the second group of lenses, the rays of light passing through the relay deformed diaphragm are changed to the third light fluxes of the second diverging angle, and the third light fluxes are output to the reflection type optical-spatial modulator element.
Therefore, the third light fluxes are respectively formed in an asymmetric shape in section. In this case, even though each second light flux is changed to the third light flux having a second diverging angle larger than the inclination angle of each micro-mirror of the reflection type optical-spatial modulator element, because a portion of the rays of light functioning as an interference component in the reflection on a micro-mirror set to an xe2x80x9conxe2x80x9d state in the reflection type optical-spatial modulator element is intercepted by the relay deformed diaphragm, any portion of each third light flux incident on the corresponding micro-mirror does not overlap with a portion of an outgoing light flux reflected on the micro-mirror.
Accordingly, the contrast of an image formed from the third light fluxes can be maintained.
Also, because each third light flux has a second diverging angle larger than the inclination angle of each micro-mirror of the reflection type optical-spatial modulator element, a size of an end plane of the light-intensity distribution uniformizing element can be enlarged. Therefore, a light receiving efficiency of the light-intensity distribution uniformizing element can be heightened. Accordingly, the brightness of the image displayed on the screen can be improved without being restricted by the inclination angle of each micro-mirror disposed on the reflection type optical-spatial modulator element.
To achieve the first subordinate object, it is preferred that the projecting optical system includes an incident-side lens for producing a projecting optical system Fourier transformation plane in which position information indicating positions of a plurality of micro-mirrors set to the xe2x80x9conxe2x80x9d state on a reflecting surface of the reflection type optical-spatial modulator element is transformed into diverging angle information indicating diverging angles of rays of a portion of third light fluxes reflected on the micro-mirrors with respect to the optical axis of the light-intensity distribution uniformizing element, a projecting optical system deformed diaphragm, disposed in the neighborhood of the projecting optical system Fourier transformation plane produced by the incident-side lens, for passing the third light fluxes reflected on the micro-mirrors of the xe2x80x9conxe2x80x9d state sent from the incident-side lens and intercepting light other than the third light fluxes according to the diverging angle information indicated by the third light fluxes, and an outgoing-side lens for outputting the third light fluxes passing through the projecting optical system deformed diaphragm to the screen.
Because the projecting optical system deformed diaphragm intercepts light other than the third light fluxes, stray light is removed from the third light fluxes. Accordingly, a contrast of the image can be improved.
To achieve the second subordinate object, it is preferred that the image displaying apparatus further includes a reflection film with an aperture, disposed on an incident end plane of the light-intensity distribution uniformizing element, for passing the first light flux through the aperture, and a sequential color recapture wheel, disposed on the outgoing end plane of the light-intensity distribution uniformizing element, for separating light of a color from the second light fluxes which are produced in the light-intensity distribution uniformizing element from the first light flux passing through the aperture of the reflection film.
Therefore, light reflected on the sequential color recapture wheel is reflected on the reflection film and passes through the sequential color recapture wheel. Accordingly, a light use efficiency can be considerably improved.
The main object is also achieved by the provision of an image displaying apparatus including a lamp light source, light changing means, a converging lens, a light-intensity distribution uniformizing element, a rely optical system, a projecting optical system and a screen.
In the light changing means, a width of light emitted from the lamp light source is changed to a first width in a first co-ordinate axial direction perpendicular to a propagation direction of the light, and the width of the light emitted from the lamp light source is changed to a second width larger than the first width in a second co-ordinate axial direction perpendicular to both the propagation direction of the light and the first co-ordinate axial direction. In the converging lens, the light changed by the light changing means is converged to a first light flux in which a diverging angle in the second co-ordinate axial direction is larger than that in the first co-ordinate axial direction. In the light-intensity distribution uniformizing element, the first light flux is changed to a plurality of second light fluxes. A diverging angle of each second light flux in the second co-ordinate axial direction is larger than that in the first co-ordinate axial direction. Intensities of the second light fluxes are equalized in an outgoing end plane of the light-intensity distribution uniformizing element, and each second light flux is output. In the relay optical system, each second light flux output from the light-intensity distribution uniformizing element is changed to a third light flux. A diverging angle of the third light flux in the second co-ordinate axial direction is larger than that in the first co-ordinate axial direction and is larger than the inclination angle of the corresponding micro-mirror of the reflection type optical-spatial modulator element. Thereafter, the third light fluxes is relayed to the reflection type optical-spatial modulator element while making the second co-ordinate axial direction be parallel to a rotation axis each micro-mirror of the reflection type optical-spatial modulator element. In the reflection type optical-spatial modulator element, the third light fluxes receive image information. Thereafter, the third light fluxes are projected onto the screen by the projecting optical system, and an image is displayed on the screen according to the image information included in the third light fluxes projected by the projecting optical system.
Therefore, each third light flux is formed in an elliptical shape in section. In this case, even though the diverging angle of the third light flux in the second co-ordinate axial direction is larger than the inclination angle of the corresponding micro-mirror of the reflection type optical-spatial modulator element, because the second co-ordinate axial direction be parallel to a rotation axis each micro-mirror of the reflection type optical-spatial modulator element, any portion of each third light flux incident on the corresponding micro-mirror does not overlap with a portion of an outgoing light flux reflected on the micro-mirror.
Accordingly, the contrast of an image formed from the third light fluxes can be maintained.
Also, because the diverging angle of the third light flux in the second co-ordinate axial direction is larger than the inclination angle of the corresponding micro-mirror of the reflection type optical-spatial modulator element, a size of an end plane of the light-intensity distribution uniformizing element can be enlarged. Therefore, a light receiving efficiency of the light-intensity distribution uniformizing element can be heightened. Accordingly, the brightness of the image displayed on the screen can be improved without being restricted by the inclination angle of each micro-mirror disposed on the reflection type optical-spatial modulator element.